Xamarin Choose Image From Gallery Path is Null

问题:

using this recipe to try and choose an image from the gallery and then upload it to s3 but my path always returns null.

private string _imgPath;
        public void InitializeMediaPicker()
        {
                Intent = new Intent();
                Intent.SetType("image/*");
                Intent.SetAction(Intent.ActionGetContent);
                StartActivityForResult(Intent.CreateChooser(Intent, "Select Picture"), 1000);
        }

        public string GetImage()
        {
            InitializeMediaPicker();

            return _imgPath;
        }

        protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
        {
            if ((requestCode != 1000) || (resultCode != Result.Ok) || (data == null)) return;
            var uri = data.Data;
            _imgPath = GetPathToImage(uri);
        }

        private string GetPathToImage(Android.Net.Uri uri)
        {
            string path = null;
            // The projection contains the columns we want to return in our query.
            var projection = new[] { Android.Provider.MediaStore.Images.Media.InterfaceConsts.Data };
            using (var cursor = ManagedQuery(uri, projection, null, null, null))
            {
                if (cursor == null) return path;
                var columnIndex = cursor.GetColumnIndexOrThrow(Android.Provider.MediaStore.Images.Media.InterfaceConsts.Data);
                cursor.MoveToFirst();
                path = cursor.GetString(columnIndex);
            }
            return path;
        }

回答1:

Here is a working implementation ported from this question and specifically, this answer.

Include the WRITE_EXTERNAL_STORAGE permission in your manifest for this code to work.

public delegate void OnImageResultHandler(bool success, string imagePath);

protected OnImageResultHandler _imagePickerCallback;
public void GetImage(OnImageResultHandler callback)
{
    if (callback == null) {
        throw new ArgumentException ("OnImageResultHandler callback cannot be null.");
    }

    _imagePickerCallback = callback;
    InitializeMediaPicker();
}

public void InitializeMediaPicker()
{
    Intent = new Intent();
    Intent.SetType("image/*");
    Intent.SetAction(Intent.ActionGetContent);
    StartActivityForResult(Intent.CreateChooser(Intent, "Select Picture"), 1000);
}

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
    if ((requestCode != 1000) || (resultCode != Result.Ok) || (data == null)) {
        return;
    }

    string imagePath = null;
    var uri = data.Data;
    try {
        imagePath = GetPathToImage(uri);
    } catch (Exception ex) {
        // Failed for some reason.
    }

    _imagePickerCallback (imagePath != null, imagePath);
}

private string GetPathToImage(Android.Net.Uri uri)
{
    string doc_id = "";
    using (var c1 = ContentResolver.Query (uri, null, null, null, null)) {
        c1.MoveToFirst ();
        String document_id = c1.GetString (0);
        doc_id = document_id.Substring (document_id.LastIndexOf (":") + 1);
    }

    string path = null;

    // The projection contains the columns we want to return in our query.
    string selection = Android.Provider.MediaStore.Images.Media.InterfaceConsts.Id + " =? ";
    using (var cursor = ManagedQuery(Android.Provider.MediaStore.Images.Media.ExternalContentUri, null, selection, new string[] {doc_id}, null))
    {
        if (cursor == null) return path;
        var columnIndex = cursor.GetColumnIndexOrThrow(Android.Provider.MediaStore.Images.Media.InterfaceConsts.Data);
        cursor.MoveToFirst();
        path = cursor.GetString(columnIndex);
    }
    return path;
}

Example Usage:

Button button = FindViewById<Button> (Resource.Id.myButton);

button.Click += delegate {
    GetImage(((b, p) => {
        Toast.MakeText(this, "Found path: " + p, ToastLength.Long).Show();
    }));
};

I've used a callback instead of returning the path for GetImage as the calling method would finish executing before OnActivityResult is called so the path returned would never be valid.

回答2:

I changed the GetPathToImage method from the Xamarin recipe to the code below and now it works!

private string GetPathToImage(Android.Net.Uri uri)
    {
        ICursor cursor = this.ContentResolver.Query(uri, null, null, null, null);
        cursor.MoveToFirst();
        string document_id = cursor.GetString(0);
        document_id = document_id.Split(':')[1];
        cursor.Close();

        cursor = ContentResolver.Query(
        Android.Provider.MediaStore.Images.Media.ExternalContentUri,
        null, MediaStore.Images.Media.InterfaceConsts.Id + " = ? ", new String[] { document_id }, null);
        cursor.MoveToFirst();
        string path = cursor.GetString(cursor.GetColumnIndex(MediaStore.Images.Media.InterfaceConsts.Data));
        cursor.Close();

        return path;
    }